I love my BP, he's very docile and sweet, but yeah, my ratsnake is much more intelligent (and she's sweet too, but I can see her "thinking" a lot more than my BP).
I don't have much to add to OP's experiences, except that we have one that's very afraid and snappy. I will make sure she knows when I open the enclosure, then I will pet her back gently before picking her up so she can adjust to the fact that I'm there and not bite me out of fear or territorialism or whatever's going on.
My other thought is that BP like burrows and dark places. Perhaps when holding yours, provide a burrow for him to go right into, like even under your shirt or a little drawstring bag. That really seems to make my bitey BP much less afraid. Then she will stick her head out and come out of her own accord rather that being abruptly taken from her enclosure to out in the open in my hands.